Lens barrel and imaging device

ABSTRACT

An interchangeable lens unit includes a second lens group unit, a focus lens unit, a fourth lens group unit, a zoom ring unit, a focus motor, and a photosensor. The zoom ring unit is arranged to mechanically transmit operational force inputted to a zoom ring to the second lens group unit and the fourth lens group unit. The focus motor is configured to electrically drive the focus lens unit in the Z axis direction with respect to the second lens group unit. The photosensor is configured to detect whether or not the focus lens unit is disposed at a starting point position with respect to the second lens group unit. The starting point position is disposed within the total movement range E of the focus lens unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Applications No.2008-219215 filed on Aug. 28, 2008. The entire disclosure of JapanesePatent Applications No. 2008-219215 is hereby incorporated herein byreference.

BACKGROUND

1. Technical Field

The technical field relates to a lens barrel with which the focal lengthcan be changed.

2. Description of the Related Art

Conventional digital cameras make use of a zoom lens system with whichthe focal length can be varied while the object distance of a subjectthat is in focus (hereinafter also referred to as the subject distance)is kept substantially constant. For example, zoom lens systems areemployed in compact digital cameras and digital cameras withinterchangeable lenses.

With a conventional lens barrel, for example, as the zoom mechanismoperates, the focus lens unit including the focus lens is moved in theoptical axis direction by a cam mechanism. This allows the focal lengthto be varied while the subject distance is kept substantially constant(see, for example, Japanese Laid-Open Patent Application 2006-113289).

A phase difference detection system has been employed as the auto-focussystem with conventional interchangeable lens digital cameras.

More recently, however, an interchangeable lens digital camera has beenproposed that makes use of a contrast detection system forauto-focusing. With this contrast detection system, for example, thefocus lens unit is moved in the optical axis direction while evaluationvalues at various positions of the focus lens unit are found on thebasis of image data. The focus lens unit is moved until the evaluationvalue goes past its peak, after which the evaluation value is returnedto its maximum position to focus the subject image (an optical image ofthe subject). Thus, in auto-focusing by contrast detection, it isnecessary to move the focus lens unit back and forth in the optical axisdirection.

Also, since the focus needs to be continued during the capture of movingpictures, the focus lens unit has to be continuously moved back andforth and the peak of the evaluation value detected.

Thus, when a contrast detection system is used, since the focus lensunit is moved in the optical axis direction, making the focus lens unitsmaller is preferable when drive speed is taken into account.

However, when a configuration is employed in which the focus lens unitis driven in the optical axis direction by a cam mechanism, as with thelens barrel described in Japanese Laid-Open Patent Application2006-113289, the focus lens unit ends up being larger or heavier.

In view of this, the inventors of the present application studied a lensbarrel with which drive of the zoom mechanism was only performed duringmanual operation by the user, and drive of the focus lens unit withrespect to the zoom mechanism was performed only by an actuator. In thiscase, because the structure of the focus lens unit and its surroundingcomponents is simplified, the focus lens unit can be smaller.

However, with this lens barrel, since the focus lens is driven by anactuator, if the user operates the zoom mechanism in a state in which nopower is supplied to the actuator, there is the possibility of asignificant discrepancy in the relationship between the zoom position ofthe optical system and the position where the focus lens unit issupposed to be. For example, if the focus lens unit needs to be moved toa specific position corresponding to the zoom position, depending on thezoom position of the optical system at the point when the power isturned on, it may take a long time for the focus lens unit to move tothe specified position.

Japanese Laid-Open Patent Application 07-199033 discloses a resettingunit for resetting the position of a lens support frame to a specificreference position on the basis of output from a step-out detection unitfor detecting step-out of the lens support frame from the actuator, buta constitution that involves reducing start-up time has yet to beproposed.

SUMMARY

It is an object to provide a lens barrel and an imaging device withwhich start-up time can be reduced.

The lens barrel according to an aspect is a lens barrel for forming anoptical image of a subject on an imaging element, comprising a firstlens unit, a second lens unit, a focus lens unit, a zoom mechanism, afocus actuator, a starting point detector, and a drive controller. Thefirst lens unit has a first lens element and a first lens support framethat supports the first lens element. The second lens unit has a secondlens element arranged to vary the focal length by moving relative to thefirst lens element in the optical axis direction, and a second lenssupport frame that supports the second lens element. The focus lens unithas a focus lens arranged to vary the focal state of the optical imageby moving relative to the first lens element or the second lens elementin the optical axis direction, and a focus lens support frame thatsupports the focus lens. The zoom mechanism relatively moves the firstlens unit and the second lens unit in the optical axis direction, andhas a zoom operating unit that is operated by the user. The zoommechanism mechanically transmits the operating force inputted to thezoom operating unit to at least one of the first lens unit and thesecond lens unit. The focus actuator is supported by the zoom mechanismto move integrally with the first lens unit, and utilizes electric powerto drive the focus lens unit in the optical axis direction with respectto the first lens unit. The starting point detector detects whether ornot the focus lens unit is disposed at a starting point position withrespect to the first lens unit. The drive controller controls the focusactuator so that the focus lens unit moves within a tracking rangeincluding the starting point position.

With this lens barrel, whether or not the focus lens unit is disposed atthe starting point position with respect to the first lens unit can bedetected by the starting point detector, and furthermore, the startingpoint position is disposed within the tracking range. The result of thisconstitution is that the drive time it takes to move the focus lens unitfrom the starting point position to a specific position within thetracking range can be made shorter. Consequently, the start-up time canbe reduced with this lens barrel and an imaging device in which thislens barrel is used.

The term “start-up time” here is the time it takes for the state of thelens barrel to move from a state in which no power is supplied to thefocus actuator to a state in which imaging is possible. The start-uptime may be, for example, the time from when the power is turned on tothe imaging device until imaging is possible, the time until imaging ispossible from the point when the operating mode is switched fromreproduction mode to imaging mode, or the time until imaging is possiblefrom the release of sleep mode.

The lens barrel here also encompasses an interchangeable lens unit thatis used in an interchangeable lens type of imaging device, in additionto a lens barrel that is integrated with a camera body. The imagingdevice also encompasses an interchangeable lens type of imaging device,in addition to an imaging device in which the camera body and the lensbarrel are integrated. Examples of possible imaging devices includedigital still cameras, interchangeable lens digital cameras, digitalvideo cameras, portable telephones with a camera function, and PDAs(Personal Digital Assistants) with a camera function. The imaging deviceencompasses devices capable of capturing only still pictures, devicescapable of capturing only moving pictures, and devices capable ofcapturing still pictures and moving pictures.

The first lens element, the second lens element, and the focus lens mayeach be made up of a plurality of lenses. Also, a state in which “thefocus actuator moves integrally with the first lens unit” encompasses astate in which the focus actuator moves with respect to the first lensunit while moving integrally overall.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of thisoriginal disclosure:

FIG. 1 is a simplified diagram of a digital camera;

FIG. 2 is a block diagram of the configuration of a camera body;

FIG. 3 is a simplified oblique view of a digital camera;

FIG. 4A is a top view of a camera body, and FIG. 4B is a rear view of acamera body;

FIG. 5 is a cross section of an interchangeable lens unit (wide angleend);

FIG. 6 is a cross section of an interchangeable lens unit (wide angleend);

FIG. 7 is a cross section of an interchangeable lens unit (telephotoend);

FIG. 8 is a cross section of an interchangeable lens unit (telephotoend);

FIG. 9 is an exploded oblique view of a second lens group unit and afocus lens unit;

FIG. 10 is an exploded oblique view of a second lens group unit and afocus lens unit;

FIG. 11 is a partial oblique view of a focus lens unit;

FIG. 12A is a diagram of the configuration of an optical system (wideangle end), and FIG. 12B is a diagram of the configuration of an opticalsystem (telephoto end);

FIG. 13 is a graph of the relationship between the rotational angle of azoom ring and the distance of the various members from an imagingsensor;

FIG. 14 is a tracking table for realizing a zoom lens system;

FIG. 15 is a cross section of an interchangeable lens unit (wide angleend);

FIG. 16 is a cross section of an interchangeable lens unit (telephotoend).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Selected embodiments will now be explained with reference to thedrawings. It will be apparent to those skilled in the art from thisdisclosure that the following descriptions of the embodiments areprovided for illustration only and not for the purpose of limiting theinvention as defined by the appended claims and their equivalents.

First Embodiment Summary of Digital Camera

A digital camera 1 will be described through reference to FIGS. 1 to 13.FIG. 1 is a simplified diagram of the digital camera 1. As shown in FIG.1, the digital camera 1 (an example of the imaging device) is a digitalcamera with an interchangeable lens, and mainly comprises a camera body3 and an interchangeable lens unit 2 (an example of the lens barrel)that is removably mounted to the camera body 3. The interchangeable lensunit 2 is mounted via a lens mount 95 to a body mount 4 provided to thefront face of the camera body 3.

FIG. 2 is a block diagram of the configuration of the camera body 3.FIG. 3 is a simplified oblique view of the digital camera 1. FIG. 4A isa top view of the camera body 3, and FIG. 4B is a rear view of thecamera body 3. FIGS. 5 to 8 are simplified cross sections of theinterchangeable lens unit 2. FIGS. 5 and 6 show the state at the wideangle end, and FIGS. 7 and 8 show the state at the telephoto end. FIG. 6is a cross section in a different plane from that of FIG. 5. FIG. 8 is across section in a different plane from that of FIG. 7. FIGS. 9 and 10are exploded oblique views of a second lens group unit 77 and a focuslens unit 75. FIGS. 12A and 12B are diagrams of the configuration of anoptical system L. FIG. 12A shows the state at the wide angle end, andFIG. 12B shows the state at the telephoto end. FIG. 13 is a graph of therelationship between the rotational position of a zoom ring 84 and thedistance of the various members from an imaging sensor 11.

In this embodiment, a three-dimensionally perpendicular coordinatesystem is set with respect to the digital camera 1. The optical axis AZof the optical system L (discussed below) coincides with the Z axisdirection (an example of the optical axis direction). The X axisdirection coincides with the horizontal direction when the digitalcamera 1 is in its portrait orientation, and the Y axis directioncoincides with the vertical direction when the digital camera 1 is inits landscape orientation. In the following description, “front” meanson the subject side of the digital camera 1 (the Z axis positivedirection side), and “rear” means the opposite side from the subjectside of the digital camera 1 (the user side, or the Z axis directionnegative side).

Interchangeable Lens Unit

The basic configuration of the interchangeable lens unit 2 will bedescribed through reference to FIGS. 1 to 12B. As shown in FIG. 1, theinterchangeable lens unit 2 has the optical system L, a lens supportmechanism 71 that supports the optical system L, a focus adjusting unit72, an aperture adjusting unit 73, a blur correction unit 74, and a lensmicrocomputer 40 (an example of the drive controller).

(1) Optical System

The optical system L is a zoom lens system for forming an optical imageof a subject, and is mainly made up of four lens groups. Morespecifically, as shown in FIGS. 12A and 12B, the optical system L has afirst lens group G1 having a positive refractive power, a second lensgroup G2 having a negative refractive power, a third lens group G3having a negative refractive power, and a fourth lens group G4 having apositive refractive power.

The first lens group G1 has a first lens L1 and a second lens L2disposed on the imaging sensor 11 side of the first lens L1. The firstlens L1 is a negative meniscus lens having a convex face that faces thesubject side. The second lens L2 is a positive meniscus lens having aconvex face that faces the subject side, and is joined to the first lensL1 via an adhesive layer.

The second lens group G2 has a third lens L3, a fourth lens L4 disposedon the imaging sensor 11 side of the third lens L3, and a fifth lens L5(an example of the first lens element) disposed on the imaging sensor 11side of the fourth lens L4. The third lens L3 is a negative meniscuslens having a convex face that faces the subject side. The fourth lensL4 is a biconcave lens. The fifth lens L5 is a biconvex lens.

The third lens group G3 is made up of a sixth lens L6 (an example of thefocus lens). The sixth lens L6 is a negative meniscus lens having aconvex face that faces the imaging sensor 11 side, and is disposed inthe Z axis direction between the fifth lens L5 and a seventh lens L7 (inthe Z axis direction between the second lens group G2 and the fourthlens group G4).

The fourth lens group G4 has the seventh lens L7 (an example of thesecond lens element), an eighth lens L8, a ninth lens L9, a tenth lensL10, an eleventh lens L11, and a twelfth lens L12. The seventh lens L7is a positive meniscus lens for blur correction, and has a convex facethat faces the imaging sensor 11 side. The eighth lens L8 is a biconvexlens. The ninth lens L9 is a biconcave lens, and is joined to the eighthlens L8 via an adhesive layer. The tenth lens L10 is a biconvex lens.The face of the tenth lens L10 on the subject side is aspherical. Theeleventh lens L11 is a negative meniscus lens having a convex face thatfaces the subject side, and is joined to the tenth lens L10 via anadhesive layer. The twelfth lens L12 is a biconvex lens.

As shown in FIGS. 12A, 12B, and 13, when zooming in from the wide angleend to the telephoto end, the first lens group G1 to fourth lens groupG4 each move in the Z axis direction along the optical axis AZ towardthe subject side. More precisely, when zooming in from the wide angleend to the telephoto end, the space between the first lens group G1 andthe second lens group G2 increases, the space between the second lensgroup G2 and the third lens group G3 increases, and the space betweenthe third lens group G3 and the fourth lens group G4 decreases. Anaperture unit 62 (discussed below) moves to the subject side along withthe fourth lens group G4.

When focusing from an infinity focal state to a close focal state, thethird lens group G3 moves along the optical axis AZ to the subject side.

Furthermore, the seventh lens L7 moves in two directions perpendicularto the optical axis AZ in order to suppress blurring in the opticalimage attributable to movement of the digital camera 1.

(2) Lens Support Mechanism

The lens support mechanism 71 is for movably supporting the opticalsystem L, and has the lens mount 95, a fixed frame 50, a cam barrel 51,a first holder 52, a first lens group support frame 53, a second lensgroup support frame 54 (an example of the first lens support frame), asecond holder 55 (an example of the first lens support frame), a thirdlens group support frame 56 (an example of the focus lens supportframe), a fourth lens group support frame 61, a zoom ring unit 83 (anexample of the zoom mechanism), and a focus ring unit 88.

The lens mount 95 is the portion of the camera body 3 that is mounted tothe body mount 4, and has a lens-side contact 91. The fixed frame 50 isa member that rotatably supports the cam barrel 51, and is fixed to thelens mount 95. The fixed frame 50 has a protrusion 50 a at the end onthe Z axis direction positive side, three concave portions 50 b providedto the outer periphery, and three linear through-grooves 50 c disposedat an equal pitch around the optical axis AZ. The cam barrel 51 hasthree convex portions 51 a provided to the inner periphery, three firstcam grooves 51 d, three second cam grooves 51 b, and three third camgrooves 51 c. Since the convex portions 51 a of the cam barrel 51 areinserted into the concave portions 50 b of the fixed frame 50, in astate in which relative movement is restricted in the Z axis direction,the cam barrel 51 is supported by the fixed frame 50 to be rotatablewith respect to the fixed frame 50.

The first lens group support frame 53 is fixed to the first holder 52and supports the first lens group G1. The first holder 52 has alongitudinal groove 52 a that is formed on the inner peripheral side andextends in the Z axis direction, and three cam pins 81 that are disposedat a constant pitch around the optical axis AZ. The protrusion 50 a ofthe fixed frame 50 is inserted in the longitudinal groove 52 a. The campins 81 are inserted in the first cam grooves 51 d of the cam barrel 51.This configuration allows the first holder 52 to move in the Z axisdirection without rotating with respect to the fixed frame 50. Theamount of movement of the first holder 52 with respect to the fixedframe 50 is determined by the shape of the first cam grooves 51 d.Female threads 52 c for attaching a conversion lens and an opticalfilter, such as a polarizing filter or a protective filter, are formedat the distal end of the first holder 52.

The second lens group support frame 54 is fixed to the second holder 55and supports the second lens group G2. The second lens group supportframe 54 and second holder 55 constitute the second lens group unit 77(an example of the first lens unit). The second holder 55 has threeconvex portions 55 b that are disposed at a constant pitch around theoptical axis AZ, and three cam pins 82 that are fixed to the convexportions 55 b. The cam pins 82 are inserted into the second cam grooves51 b. The convex portions 55 b are inserted into the linearthrough-grooves 50 c of the fixed frame 50. This configuration allowsthe second lens group support frame 54 and the second holder 55 to movein the Z axis direction without rotating with respect to the fixed frame50. The amount of movement of the second lens group support frame 54 andthe second holder 55 with respect to the fixed frame 50 is determined bythe shape of the second cam grooves 51 b.

The third lens group support frame 56 is a member that supports thethird lens group G3 (more precisely, the sixth lens L6 that functions asa focus lens), and has a bearing part 56 a, an anti-rotation part 56 b,a rack support 56 c, and a protrusion 56 d. The sixth lens L6 and thethird lens group support frame 56 constitute the focus lens unit 75. Thesecond holder 55 supports the front ends of two guide poles 63 a and 63b that extend in the Z axis direction. A guide pole support plate 65 isa member for supporting the rear end of the guide pole 63 a, and isfixed on the imaging sensor 11 side of the second holder 55. The guidepole 63 a is inserted into the bearing part 56 a, and the guide pole 63b is inserted into the anti-rotation part 56 b. The third lens groupsupport frame 56 is supported movably in the Z axis direction by theguide poles 63 a and 63 b while being restricted in rotation around theoptical axis AZ.

The rack support 56 c is a member that extends from the bearing part 56a to the Z axis direction negative side, and supports a rack 66rotatably and movably integrally in the axial direction. The rack 66 hasa rack main body 66 a having a plurality of teeth 66 c, and a shaft 66 bthat extends in the Z axis direction. The plurality of teeth 66 c meshwith a lead screw 64 a of a focus motor 64. The shaft 66 b is supportedby the rack support 56 c, so the rack 66 is able to rotate around thecenter axis R with respect to the rack support 56 c.

As shown in FIGS. 9 and 11, a torsion coil spring 68 is attached to therack support 56 c. The torsion coil spring 68 has a wound portion 68 athat generates elastic force, a first end 68 b, and a second end 68 c.The wound portion 68 a is fitted to the shaft 66 b of the rack 66. Withthe wound portion 68 a twisted, the first end 68 b is hooked onto therack support 56 c, while the second end 68 c is hooked onto the rack 66.That is, the torsion coil spring 68 imparts rotational force in an Adirection to the rack 66, and constantly presses the rack 66 against thelead screw 64 a This reduces backlash between the rack 66 and the leadscrew 64 a, and increases the positional accuracy of the focus lens unit75. Also, since the rack 66 is constantly pressed against the lead screw64 a, drive force can be more efficiently transmitted from the leadscrew 64 a to the rack 66.

The wound portion 68 a of the torsion coil spring 68 is also compressedin the Z axis direction (the direction parallel to the center axis R)between the rack support 56 c and the rack 66. The torsion coil spring68 imparts a pressing force F to the rack 66, and the torsion coilspring 68 presses the rack 66 against the rack support 56 c. Thisreduces movement of the rack 66 in the Z axis direction with respect tothe rack support 56 c, and further improves the positional accuracy ofthe focus lens unit 75.

The focus motor 64 (an example of the focus actuator) is fixed to thesecond holder 55. The focus motor 64 is a stepping motor, for example.The focus motor 64 has the lead screw 64 a as its rotational shaftextending in the Z axis direction. This lead screw 64 a meshes with therack 66.

The protrusion 56 d is a portion for detecting the starting point of thefocus lens unit 75, and is provided at a location that can pass throughthe detection region of a photosensor 67 (discussed below). In thisembodiment, since the third lens group G3 (a focus lens group) is formedby the single sixth lens L6, the weight of the third lens group G3 canbe 1 g or less, for example, which allows the drive speed with the focusmotor 64 to be higher.

The fourth lens group support frame 61 (an example of the second lenssupport frame) has a first support frame 57, a second support frame 58,a third support frame 59, and a fourth support frame 60. The fourth lensgroup G4 and the fourth lens group support frame 61 constitute a fourthlens group unit 78 (an example of the second lens unit).

The first support frame 57 supports the seventh lens L7. The secondsupport frame 58 supports the eighth lens L8 and the ninth lens L9, andalso supports the first support frame 57 movably in two directionsperpendicular to the optical axis AZ. The second support frame 58 hasthree cam pins 80 that are disposed at a constant pitch around theoptical axis AZ.

The third support frame 59 supports the tenth lens L10 and the eleventhlens L11, and is fixed by screws, for example, to the second supportframe 58. The fourth support frame 60 supports the twelfth lens L12, andis fixed by screws, for example, to the third support frame 59. Becauseof their configuration, the first support frame 57, the second supportframe 58, the third support frame 59, and the fourth support frame 60move integrally along the optical axis AZ.

The first support frame 57 is supported by the second support frame 58so as to be movable in two directions perpendicular to the optical axisAZ, for example. This configuration allows the first support frame 57 tomove integrally in the Z axis direction with respect to the secondsupport frame 58, the third support frame 59, and the fourth supportframe 60, while allowing movement in a direction perpendicular to theoptical axis AZ.

The zoom ring unit 83 has a ring base 86, the zoom ring 84 (an exampleof the zoom operating unit), and a linear position sensor 87 thatdetects the rotational position of the zoom ring 84. The “rotationalposition of the zoom ring 84” refers to the position of the zoom ring 84in the rotational direction, and can also be considered to be therotational angle of the zoom ring 84 from a reference position.

The zoom ring 84 has a cylindrical shape, and is supported by the ringbase 86 fixed to the fixed frame 50, so as to be movable around theoptical axis AZ in a state in which movement in the Z axis direction isrestricted. The zoom ring 84 has a through-hole 84 a at the end on the Zaxis direction negative side. A zoom drive pin 85 that is fixed to thecam barrel 51 is inserted into the through-hole 84 a. Consequently, thecam barrel 51 rotates integrally with the zoom ring 84 around theoptical axis AZ.

The linear position sensor 87 detects the rotational position androtational direction in which the user has put the zoom ring 84, andsends the detection result to the lens microcomputer 40. Morespecifically, the linear position sensor 87 is fixed to the ring base 86and has a slider 87 a that protrudes outward in the radial direction.This slider 87 a is inserted into a cam groove 84 b formed in the zoomring 84. When the zoom ring 84 is rotated with respect to the fixedframe 50, the slider 87 a moves in the Z axis direction along the camgroove 84 b. The linear position sensor 87 has a varistor, and when theslider 87 a sliders over a magnetic resistor that is inside thisvaristor, output (output voltage) that is proportional to the positionof the slider 87 a in the Z axis direction can be obtained linearlybetween terminals at both ends to which a specific voltage has beenapplied. The output of the linear position sensor 87 is converted intorotational position information, which allows the rotational position ofthe zoom ring 84 to be detected. The focal length of the optical systemL is displayed on the outer peripheral face of the zoom ring 84.

Since the first lens group G1 to fourth lens group G4 are mechanicallylinked via the lens support mechanism 71, the absolute positions of thefirst lens group G1 to fourth lens group G4 (such as their positionsusing a light receiving face 11 a of the imaging sensor 11 as areference) have a specific relationship to the rotational position ofthe zoom ring 84. Therefore, if the rotational position of the zoom ring84 is detected, the absolute positions of the first lens group G1 tofourth lens group G4 with respect to the lens mount 95 can beascertained. The zoom ring 84 may have another structure instead, suchas a movable lever.

The focus ring unit 88 has a focus ring 89 and a focus ring angledetector 90 that detects the rotational angle of the focus ring 89. Thefocus ring 89 has a cylindrical shape, and is supported by the ring base86 rotatably around the optical axis AZ in a state in which movement inthe Z axis direction is restricted. The rotational angle and rotationalposition of the focus ring 89 can be detected by the focus ring angledetector 90. The focus ring angle detector 90 has two photosensors (notshown), for example. The focus ring 89 has a plurality of protrusions 89a that protrude inward in the radial direction and are disposed atequidistant spacing in the rotational direction. Each of thesephotosensors has a light emitting part (not shown) and a light receivingpart (not shown), and the plurality of protrusions 89 a pass in betweenthe light emitting parts and the light receiving parts, allowing therotational angle and rotational direction of the focus ring 89 to bedetected. The focus ring 89 may have another structure instead, such asa movable lever.

(3) Focus Adjusting Unit

The focus adjusting unit 72 has the focus motor 64, a focus drivecontroller 41, and the photosensor 67 (an example of the positionsensor). The focus motor 64 is fixed to the second holder 55 and drivesthe focus lens unit 75 in the Z axis direction with respect to thesecond lens group unit 77. The drive of the focus lens unit 75 withrespect to the second lens group unit 77 is performed by the focus motor64 alone. In other words, in a state in which the focus motor 64 is notdriving the focus lens unit 75 (such as when no power is being suppliedto the focus motor 64), the focus lens unit 75 cannot be moved withrespect to the second lens group unit 77. In this case, the focus lensunit 75 moves in the Z axis direction integrally with the second holder55.

The lead screw 64 a of the focus motor 64 rotates on the basis of adrive signal inputted from the focus drive controller 41. The rotarymotion generated by the focus motor 64 is converted by the lead screw 64a and the rack 66 into linear motion of the focus lens unit 75 in the Zaxis direction. Consequently, the focus lens unit 75 can move in the Zaxis direction with respect to the second lens group unit 77.

With this digital camera 1, to achieve a zoom lens system with which thefocal length can be varied while keeping the subject distancesubstantially constant, the focus lens unit 75 is driven by the focusadjusting unit 72 on the basis of a tracking table stored ahead of timein the lens microcomputer 40. This type of tracking is called electronictracking here.

The tracking table contains information indicating the position of thefocus lens unit 75 where the focused subject distance remainssubstantially constant even if the focal length changes (more precisely,the position of the focus lens unit 75 with respect to the second lensgroup unit 77). The phrase “the subject distance remains substantiallyconstant” means that the amount of change in the subject distance fallswithin a specific subject field depth. Electronic tracking will bediscussed below.

Referring to FIG. 9, the photosensor 67, which detects the startingpoint position of the focus lens unit 75, is installed in the secondholder 55. This photosensor 67 has a light emitting part (not shown) anda light receiving part (not shown). When the protrusion 56 d of thethird lens group support frame 56 passes between the light emitting partand the light receiving part, the photosensor 67 can detect the presenceof the protrusion 56 d. That is, the starting point position of thefocus lens unit 75 with respect to the second lens group unit 77 can bedetected by the photosensor 67. In other words, the photosensor 67 is astarting point detector that detects the starting point position of thethird lens group G3 with respect to the second lens group G2. The lensmicrocomputer 40 drives the third lens group G3 to the starting pointposition, and checks whether the focus lens unit 75 (the third lensgroup G3) is in the starting point position by using a signal from thephotosensor 67.

The starting point position that can be detected by the photosensor 67is an absolute position that never moves with respect to the second lensgroup unit 77. Accordingly, when the position of the focus lens unit 75is reset to the starting point position with respect to the second lensgroup unit 77, the photosensor 67 drives the focus lens unit 75 to theposition where the protrusion 56 d for starting point detection isdetected. When the power switch 25 is turned off, the focus lens unit 75is driven by the focus motor 64 to a position where the protrusion 56 dof the third lens group 56 is detected by the photosensor 67 regardlessof the position of focus lens unit 75, for example. Upon completion ofthe drive of the focus lens unit 75, the power supply to the digitalcamera 1 is halted. Conversely, when a power switch 25 of the digitalcamera 1 is turned on, the focus motor 64 drives the focus lens unit 75to a specific position determined on the basis of the tracking table.The starting point detector is not limited to being a photosensor, andmay instead be a combination of a magnet and a magnetic sensor, forexample.

(4) Aperture Adjusting Unit

The aperture adjusting unit 73 has the aperture unit 62 fixed to thesecond support frame 58, an aperture drive motor (not shown) that drivesthe aperture unit 62, and an aperture drive controller 42 that controlsthe aperture drive motor. The aperture drive motor is a stepping motor,for example. The aperture drive motor is driven on the basis of a drivesignal inputted from the aperture drive controller 42. The drive forcegenerated by the aperture drive motor drives aperture blades 62 a in theopening and closing directions. The aperture value of the optical systemL can be changed by driving the aperture blades 62 a.

(5) Blur Correction Unit

The blur correction unit 74 is for reducing blurring of the opticalimage attributable to movement of the interchangeable lens unit 2 andthe camera body 3, and has an electromagnetic actuator 46, a positiondetecting sensor 47, and a blur correction microcomputer 48.

The electromagnetic actuator 46 drives the first support frame 57 in adirection perpendicular to the optical axis AZ. More specifically, theelectromagnetic actuator 46 has a magnet (not shown) and a coil (notshown), for example. For instance, the coil is provided to the firstsupport frame 57, and the magnet is fixed to the second support frame58.

The position detecting sensor 47 is for detecting the position of thefirst support frame 57 with respect to the second support frame 58, andis a hole element, for example. A movement detecting sensor (not shown)such as a gyro sensor is installed in the interchangeable lens unit 2.The blur correction microcomputer 48 controls the electromagneticactuator 46 on the basis of the detection result of the positiondetecting sensor 47 and the detection result of the movement detectingsensor. Consequently, blurring of the optical image attributable tomovement of the digital camera 1 can be reduced.

Reducing blurring of the subject image may instead be accomplished byelectronic blur correction, in which blurring that appears in an imageis corrected on the basis of image data outputted from the imagingsensor 11. Also, blurring of the subject image may be reduced by asensor shift method in which the imaging sensor 11 is driven in twodirections perpendicular to the optical axis AZ.

(6) Lens Microcomputer

The lens microcomputer 40 has a CPU (not shown), a ROM (not shown), anda memory 40 a, and various functions can be performed by readingprograms stored in the ROM into the CPU. For instance, the lensmicrocomputer 40 can check whether the focus lens unit 75 is in thestarting point position by using a detection signal from the photosensor67.

The memory 40 a is a nonvolatile memory, and can hold stored informationeven when no power is being supplied. The memory 40 a contains atracking table (discussed below) for realizing a zoom lens system, orinformation related to the interchangeable lens unit 2 (lensinformation), for example. The lens microcomputer 40 controls the focusmotor 64, and the focus lens unit 75 is driven by the focus motor 64 inthe Z axis direction, on the basis of this tracking table. An operationin which the position of the focus lens unit 75 is made to conform tochanges in the focal length on the basis of a tracking table willhereinafter be referred to as electronic tracking.

The lens microcomputer 40 has a counter 40 b for counting the number ofpulses of the focus motor 64. The counter 40 b is set to a count of “+1”when the focus lens unit 75 is driven to the Z axis direction positiveside, and to a count of “−1” when the focus lens unit 75 is driven tothe Z axis direction negative side. The lens microcomputer 40 canascertain the relative position of the third lens group G3 with respectto the second lens group G2 (the position of the focus lens unit 75 withrespect to the second lens group unit 77) by thus counting the number ofdrive pulses of the focus motor 64.

For example, the rack 66 is driven by 0.6 mm in the Z axis direction forevery rotation of the lead screw 64 a of the focus motor 64. If thefocus motor 64, which has a 10-pole magnet, is driven by 1-2 phaseexcitation, then the rack 66 is driven in the Z axis direction by0.6/20/2=0.015 mm (15 μm) per pulse. During micro-step drive, the rack66 can be driven in even finer units. Using a stepping motor allows thefocus lens unit 75 to be driven in fine units, and reduces backlashduring reverse drive, for example. That is, selecting a stepping motoras the focus motor 64 affords very precise focus adjustment. Also,counting the number of drive pulses allows the current position of thefocus lens unit 75 with respect to the second lens group unit 77 to beascertained, and allows the amount of drive of the focus lens unit 75 tobe calculated.

Camera Body

The basic configuration of the camera body 3 will be described throughreference to FIGS. 1 to 4B. As shown in FIGS. 1 to 4B, the camera body 3has a case 3 a, a body mount 4, an operating unit 39, an imageacquisition unit 35, an image display unit 36, a viewfinder unit 38, abody microcomputer 10 (an example of the drive controller, and anexample of the auxiliary operation detector), and a battery 22 (anexample of the main power supply).

(1) Case

The case 3 a constitutes the outer part of the camera body 3. As shownin FIGS. 4A and 4B, the body mount 4 is provided to the front face ofthe case 3 a, and the operating unit 39 is provided to the rear and topfaces of the case 3 a. More specifically, a display unit 20, the powerswitch 25, a mode selector dial 26, a navigation key 27, a menu settingbutton 28, a setting button 29, a mode selector button 34, and a movingpicture capture operation button 24 are provided to the rear face of thecase 3 a. A shutter button 30 is provided to the top face of the case 3a.

(2) Body Mount

The body mount 4 is the portion of the interchangeable lens unit 2 wherethe lens mount 95 is mounted, and has a body-side contact (not shown)that can be electrically connected with the lens-side contact 91. Thecamera body 3 is able to send and receive data to and from theinterchangeable lens unit 2 via the body mount 4 and the lens mount 95.For example, the body microcomputer 10 (discussed below) sends the lensmicrocomputer 40 a control signal, such as an exposure synchronizationsignal, via the body mount 4 and the lens mount 95.

(3) Control Unit

As shown in FIGS. 4A and 4B, the operating unit 39 has various controlsthat the user can use to input operating information. For instance, thepower switch 25 is a switch for turning the power on and off to thedigital camera 1 or the camera body 3. When the power is turned on withthe power switch 25, power is supplied to the various parts of thecamera body 3 and the interchangeable lens unit 2.

The mode selector dial 26 is used to switch the operating mode, such asstill picture capture mode, moving picture capture mode, or reproductionmode, and the user can turn the mode selector dial 26 to switch theoperating mode. When the still picture capture mode is selected with themode selector dial 26, the operating mode is switched to the stillpicture capture mode, and when the moving picture capture mode isselected with the mode selector dial 26, the operating mode is switchedto the moving picture capture mode. In the moving picture capture mode,basically moving picture capture is possible. When the reproduction modeis selected with the mode selector dial 26, the operating mode isswitched to the reproduction mode, allowing the captured image to bedisplayed on the display unit 20.

The navigation key 27 is used to select the left, right, up, and downdirections. The user can use the navigation key 27 to select the desiredmenu from various menu screens displayed on the display unit 20, forexample.

The menu setting button 28 is for setting the various operations of thedigital camera 1. The setting button 29 is for executing the operationsof the various menus.

The moving picture capture operation button 24 is for starting andstopping the capture of moving pictures. Even if the operating modeselected with the mode selector dial 26 is the still picture capturemode or the reproduction mode, when the moving picture capture operationbutton 24 is pressed, the operating mode is forcibly changed to themoving picture capture mode, and moving picture capture begins,regardless of the setting on the mode selector dial 26. When this movingpicture capture operation button 24 is pressed during the capture of amoving picture, the moving picture capture ends and the operating modechanges to the one selected on the mode selector dial 26, that is, tothe one prior to the start of moving picture capture. For example, ifthe still picture capture mode has been selected with the mode selectordial 26 when the moving picture capture operation button 24 is pressed,the operating mode automatically changes to the still picture capturemode after the moving picture capture operation button 24 is pressedagain.

The shutter button 30 is pressed by the user to capture an image. Whenthe shutter button 30 is pressed, a timing signal is outputted to thebody microcomputer 10. The shutter button 30 is a two-stage switch thatcan be pressed half way down or all the way down. Light measurement andranging are commenced when the user presses the button half way down.When the user presses the shutter button 30 all the way down in a statein which the shutter button 30 has been pressed half way down, a timingsignal is outputted, and image data is acquired by the image acquisitionunit 35.

The macro imaging switch button 23 is used to switch between normalimaging and macro imaging. For instance, when the user presses the macroimaging switch button 23, a tracking table corresponding to 0.3 m, whichis the minimum subject distance, is automatically selected by the lensmicrocomputer 40.

As shown in FIG. 1, a lens attachment button 99 (an example of the lensattachment operating unit) for attaching and removing theinterchangeable lens unit 2 to and from the camera body 3 is provided tothe front face of the camera body 3. The lens attachment button 99 has acontact (not shown) that is in its “on” state when the button is pressedby the user, for example, and is electrically connected to the bodymicrocomputer 10. When the lens attachment button 99 is pressed, thebuilt-in contact is switched on, and the body microcomputer 10recognizes that the lens attachment button 99 has been pressed.

(4) Image Acquisition Unit

The image acquisition unit 35 mainly comprises the imaging sensor 11 (anexample of the imaging element) such as a CCD (Charge Coupled Device)that performs opto-electrical conversion, a shutter unit 33 that adjuststhe exposure state of the imaging sensor 11, a shutter controller 31that controls the drive of the shutter unit 33 on the basis of a controlsignal from the body microcomputer 10, and an imaging sensor drivecontroller 12 that controls the operation of the imaging sensor 11.

The imaging sensor 11 is a CCD (Charge Coupled Device) sensor, forexample, that converts the optical image formed by the optical system Linto an electrical signal. The imaging sensor 11 is driven andcontrolled on the basis of timing signals generated by the imagingsensor drive controller 12. The imaging sensor 11 may instead be a CMOS(Complementary Metal Oxide Semiconductor) sensor.

The shutter controller 31 drives a shutter drive actuator 32 andoperates the shutter unit 33 according to a control signal outputtedfrom the body microcomputer 10 that has received a timing signal.

The auto-focusing method that is employed in this embodiment is acontrast detection method that makes use of image data produced by theimaging sensor 11. Using a contrast detection method allowshigh-precision focal adjustment.

(5) Body Microcomputer

The body microcomputer 10 is a control device that is the command centerof the camera body 3, and controls the various components of the digitalcamera 1 according to operation information inputted to the operationunit 39. More specifically, the body microcomputer 10 is equipped with aCPU, ROM, and RAM, and the programs held in the ROM are read by the CPU,allowing the body microcomputer 10 to perform a variety of functions.For instance, the body microcomputer 10 has the function of detectingthat the interchangeable lens unit 2 has been mounted to the camera body3, or the function of acquiring information about controlling thedigital camera 1, such as information about the focal length from theinterchangeable lens unit 2.

The body microcomputer 10 is able to receive signals from the powerswitch 25, the shutter button 30, the mode selector dial 26, thenavigation key 27, the menu setting button 28, and the setting button29. Various information related to the camera body 3 is held in a memory10 a inside the body microcomputer 10. The memory 10 a is a nonvolatilememory, and can hold stored information even when no power is beingsupplied.

Also, the body microcomputer 10 periodically produces a verticalsynchronization signal, and produces an exposure synchronization signalon the basis of the vertical synchronization signal in parallel with theproduction of the vertical synchronization signal. The bodymicrocomputer 10 can produce an exposure synchronization signal, sincethe body microcomputer 10 ascertains beforehand the exposure starttiming and the exposure stop timing based on the verticalsynchronization signal. The body microcomputer 10 outputs a verticalsynchronization signal to a timing generator (not shown), and outputs anexposure synchronization signal at a specific period to the lensmicrocomputer 40 via the body mount 4 and the lens mount 95. The lensmicrocomputer 40 acquires position information about the focus lens unit75.

The imaging sensor drive controller 12 produces an electronic shutterdrive signal and a read signal of the imaging sensor 11 at a specificperiod on the basis of the vertical synchronization signal. The imagingsensor drive controller 12 drives the imaging sensor 11 on the basis ofthe electronic shutter drive signal and the read signal. That is, theimaging sensor 11 reads to a vertical transfer part (not shown) theimage data produced by numerous opto-electrical conversion element (notshown) present in the imaging sensor 11, according to the read signal.

The body microcomputer 10 also controls the focus adjusting unit 72(discussed below) via the lens microcomputer 40.

The image signal outputted from the imaging sensor 11 is sent from ananalog signal processor 13 and successively processed by an A/Dconverter 14, a digital signal processor 15, a buffer memory 16, and animage compressor 17. The analog signal processor 13 subjects the imagesignal outputted from the imaging sensor 11 to gamma processing or othersuch analog signal processing. The A/D converter 14 converts the analogsignal outputted from the analog signal processor 13 into a digitalsignal. The digital signal processor 15 subjects the image signalconverted into a digital signal by the A/D converter 14 to digitalsignal processing such as noise elimination or contour enhancement. Thebuffer memory 16 is a RAM (Random Access Memory), and temporarily storesthe image signal. The image signal stored in the buffer memory 16 issent to and processed by first the image compressor 17 and then an imagerecorder 18. The image signal stored in the buffer memory 16 is read ata command from an image recording controller 19 and sent to the imagecompressor 17. The data of the image signal sent to the image compressor17 is compressed into an image signal according to a command from theimage recording controller 19. This compression adjusts the image signalto a smaller data size than that of the original data. An example of themethod for compressing the image signal is the JPEG (Joint PhotographicExperts Group) method in which compression is performed on the imagesignal for each frame. After this, the compressed image signal isrecorded by the image recording controller 19 to the image recorder 18.When a moving picture is recorded, JPEG was used to compress a pluralityof image signals, compressing an image signal for each frame, and anH.264/AVC method can also be used, in which compression is performed onimage signals for a plurality of frames all at once.

The image recorder 18 produces a still picture file or moving picturefile that is associated with specific information to be recorded withthe image signal. The image recorder 18 also records the still picturefile or moving picture file on the basis of a command from the imagerecording controller 19. The image recorder 18 is a removable memoryand/or an internal memory, for example. The specific information to berecorded with the image signal includes the date the image was captured,focal length information, shutter speed information, aperture valueinformation, and photography mode information. Still picture files arein Exif (TRADEMARK) format or a format similar to Exif (TRADEMARK)format. Moving picture files are in H.264/AVC format or a format similarto H.264/AVC format.

(6) Image Display Unit

The image display unit 36 has the display unit 20 and an image displaycontroller 21. The display unit 20 is a liquid crystal monitor, forexample. The display unit 20 displays as a visible image the imagesignal recorded to the buffer memory 16 or the image recorder 18 on thebasis of a command from the image display controller 21. Possibledisplay modes on the display unit 20 include a display mode in whichonly the image signal is displayed as a visible image, and a displaymode in which the image signal and information from the time of captureare displayed as a visible image.

(7) Viewfinder

The viewfinder unit 38 has a liquid crystal viewfinder 8 that displaysthe image acquired by the imaging sensor 11, and a viewfinder eyepiecewindow 9 provided to the rear face of the case 3 a. The user looks intothe viewfinder eyepiece window 9 to view the image displayed on theliquid crystal viewfinder 8.

(8) Battery

The battery 22 supplies power to the various components of the camerabody 3, and also supplies power to the interchangeable lens unit 2 viathe lens mount 95. In this embodiment, the battery 22 is a rechargeablebattery. The battery 22 may be a dry cell, or may be an external powersupply, with which power is supplied from the outside through a powercord.

Tracking Table

With the digital camera 1, electronic tracking is performed by the focusadjusting unit 72 so that the focal length can be varied while thesubject distance is kept substantially constant. More specifically, asshown in FIG. 14, to perform electronic tracking, a tracking table 100is held in the memory 40 a. This tracking table 100 shows therelationship between the rotational position of the zoom ring 84 and theposition of the focus lens unit 75 in the Z axis direction with respectto the second lens group unit 77. For example, the memory 40 a holdsthree tracking tables 100 corresponding to subject distances of 0.3 m,1.0 m, and infinity (∞). The infinity is an example of a first subjectdistance.

The tracking table 100 consists of discrete information in which therotational position of the zoom ring 84 and the position of the focuslens unit 75 in the Z axis direction are divided into several groups. Ingeneral, the number of divisions is determined so that the subjectdistance will fit within a specific subject field depth even if the zoomring 84 is turned.

The rotational position of the zoom ring 84 (position in the rotationaldirection) can be detected by the linear position sensor 87. On thebasis of this detection result and the tracking table 100, the lensmicrocomputer 40 can determine the position of the focus lens unit 75 inthe Z axis direction with respect to the second lens group unit 77.

The starting point position D of the focus lens unit 75 with respect tothe second lens group unit 77 is detected by the photosensor 67, whichis indicated by the one-dot chain line in FIG. 14. The focus lens unit75 is able to move within a range from a position E1 to a position E2,on the basis of all the tracking tables. In this embodiment, thestarting point position D is located in the middle of the total movementrange E, within the total movement range E of the focus lens unit 75(between positions E1 and E2). Thus disposing the starting pointposition D in the middle of the total movement range E allows the focuslens unit 75 to be moved relatively quickly to any position when thepower is turned on to the digital camera 1, for example. Consequently,the start-up time for switching the state of the digital camera 1 from astopped state to an imaging enabled state can be reduced.

As shown in FIG. 14, the starting point position D is disposed within amovement range G (between a position E2 and a position H1; an example ofthe first tracking range) of the focus lens unit 75 on the basis of theinfinity tracking table 100. In general, the user is most likely tocapture an image of a subject at the infinity position when turning onthe power to the digital camera 1 and capturing an image of the subject,so the start-up time can be shortened by disposing the starting pointposition D within the movement range G.

The movement range G of the focus lens unit 75 based on the infinitytracking table 100 includes a movement range H from a position H2 (anexample of the first position) to a position H1 (an example of thesecond position). The position H2 is the position of the focus lens unit75 at which the optical system L can focus on infinity at the wide angleend. When the focus motor 64 is controlled by the lens microcomputer 40on the basis of the infinity tracking table 100 in a state in which therotational position of the zoom ring 84 corresponds to the wide angleend, the focus lens unit 75 moves to the position H2. The position H1 isthe position where the focus lens unit 75 is farthest away from theimaging sensor 11 when the focus lens unit 75 is driven on the basis ofthe infinity tracking table 100.

The starting point position D is disposed in the middle of this movementrange H. In general, the optical system L is most likely to be at thewide angle end when the user turns on the power to the digital camera 1to capture an image of a subject, so the start-up time can be furtherreduced by disposing the starting point position D in the middle of themovement range H.

The tracking table 100 may also be expressed by a polynomial, ratherthan discrete information divided into several groups. Positioninformation about the first lens group G1, second lens group G2, orfourth lens group G4 in the Z axis direction may also be used instead ofthe rotational position of the zoom ring 84. The “position of the focuslens unit 75 in the Z axis direction with respect to the second lensgroup unit 77” can be rephrased as the position of the third lens groupG3 in the Z axis direction with respect to the second lens group unit77, or the position of the third lens group G3 in the Z axis directionwith respect to the second lens group G2.

Operation of the Digital Camera

The operation of the digital camera 1 will be described.

(1) Imaging Mode

This digital camera 1 has two imaging modes. More specifically, thedigital camera 1 has a viewfinder imaging mode in which the user looksthrough the viewfinder eyepiece window 9 to view the subject, and amonitor imaging mode in which the user observes the subject on thedisplay unit 20.

With the viewfinder imaging mode, the image display controller 21 drivesthe liquid crystal viewfinder 8, for example. As a result, an image ofthe subject (a so-called through-image) acquired by the imaging sensor11 is displayed on the liquid crystal viewfinder 8.

With the monitor imaging mode, the display unit 20 is driven by theimage display controller 21, for example, and a real-time image of thesubject is displayed on the display unit 20. Switching between these twoimaging modes can be performed with the mode selector button 34.

(2) Zoom Operation

Next, the operation of the interchangeable lens unit 2 when the userperforms zooming will be described.

When the user rotates the zoom ring 84, the cam barrel 51 rotates alongwith the zoom ring 84. When the cam barrel 51 rotates around the opticalaxis AZ, the first holder 52 is guided by the first cam grooves 51 d ofthe cam barrel 51, and advances in the Z axis direction. The secondholder 55 and the fourth lens group support frame 61 are also guided bythe second cam grooves 51 b and the third cam grooves 51 c of the cambarrel 51, and advance in the Z axis direction. Thus, by rotating thezoom ring 84, the state of the interchangeable lens unit 2 can bechanged from the wide angle end state shown in FIGS. 5 and 6 to thetelephoto end state shown in FIGS. 7 and 8. Consequently, the subjectcan be imaged at the desired zoom position by adjusting the rotationalposition of the zoom ring 84.

The second holder 55 is mechanically driven in the Z axis direction byrotating the zoom ring 84 here, but only the focus lens unit 75 iselectrically driven and controlled by the focus adjusting unit 72 on thebasis of the tracking table 100 stored ahead of time in the memory 40 a,so that the subject distance remains substantially constant. Forexample, when the focus lens unit 75 is driven by the focus motor 64 onthe basis of the tracking table 100, the focal state can be kept atinfinity both when the move is from the wide angle end to the telephotoend, and when the move is from the telephoto end to the wide angle end.

More precisely, when the zoom ring 84 is turned, the first lens groupG1, the second lens group G2, the third lens group G3, and the fourthlens group G4 move in the Z axis direction along the optical axis AZ.Consequently, the magnification of the subject image changes. At thispoint the third lens group G3 also moves in the Z axis direction alongthe optical axis AZ in a state of being supported by the second holder55 via the third lens group support frame 56. When there is a relativechange in the positional relationship of the first lens group G1, thesecond lens group G2, the third lens group G3, and the fourth lens groupG4, the focal state of the subject image formed on the imaging sensor 11also changes. That is, the subject distance at which the focal point isformed on the imaging sensor 11 changes.

In view of this, with the digital camera 1, even if the focal lengthchanges, the subject distance can be kept substantially constant bydriving the focus motor 64 according to the rotational position of thezoom ring 84. More specifically, using just the focus motor 64, thefocus lens unit 75 including the third lens group G3 is driven withrespect to the second lens group unit 77. The lens microcomputer 40acquires the rotational position of the zoom ring 84 on the basis of thedetection signal of the linear position sensor 87. At the same time, thelens microcomputer 40 calculates the position of the focus lens unit 75with respect to the second lens group unit 77 from the count value atthe counter 40 b. Utilizing the plurality of tracking tables 100 shownin FIG. 14, the lens microcomputer 40 finds the current subject distancefrom these two pieces of information (the current rotational position ofthe zoom ring 84, and the position of the focus lens unit 75 withrespect to the second lens group unit 77), and selects the trackingtable 100 corresponding to the subject distance thus found. Here, wewill assume that the tracking table 100 corresponding to infinity wasselected.

Next, the lens microcomputer 40 again acquires the rotational positionof the zoom ring 84, and finds the rotational speed of the zoom ring 84,that is, the rate of change in the focal length, from the amount ofchange in the rotational position of the zoom ring 84.

Next, the lens microcomputer 40 predicts the rotational position of thezoom ring 84 after the elapse of a specific time from the currentrotational angle of the zoom ring 84 and the rotational speed of thezoom ring 84, and finds as a target position the position of the focuslens unit 75 in the Z axis direction corresponding to the predictedrotational position of the zoom ring 84. After the elapse of a specifictime, the lens microcomputer 40 drives the focus motor 64 via the focusdrive controller 41 so that the focus lens unit 75 will be located atthis target position. Consequently, the focus lens unit 75 is driven soas to follow the movement of the other lens groups, and the subjectdistance is kept constant.

Thus, in the electronic tracking operation, the lens microcomputer 40predicts the change in the focal length that will accompany zoomingoperation, and acquires from the tracking table 100 the target positionof the focus lens unit 75 corresponding to the predicted focal length.The focus lens unit 75 is driven to the target position by the focusmotor 64 in parallel with the zooming operation of the optical system L.Since this operation is executed at specific time intervals, even if thezoom ring 84 is rotated and the focal length of the optical system Lchanges, the focus lens unit 75 will move to the Z axis directionposition corresponding to the focal length on the basis of the trackingtable 100, and the drive of the focus lens unit 75 can conform to thechange in the focal length. Consequently, the subject distance can bekept substantially constant regardless of any change in the focallength. The control of these components may be performed by the bodymicrocomputer 10, rather than lens microcomputer 40.

Similarly, when the focused subject distance is short, such as 1 m, forexample, the tracking table 100 for which the subject distance is 1 m isselected, and both when the move is from the wide angle end to thetelephoto end, and when the move is from the telephoto end to the wideangle end, the focused state at a short distance can be maintained bydriving the focus motor 64, and the zooming operation can be carried outsmoothly.

In particular, since the focus lens unit 75 and the focus motor 64 movein the Z axis direction integrally with the second lens group unit 77,even if the user turns the zoom ring 84 quickly, the focus lens unit 75can still be moved integrally with the second lens group unit 77.Therefore, if the subject distance is to be kept substantially constantbefore and after the zooming operation, the focus motor 64 may move thethird lens group G3 by a distance obtained by subtracting the distancethat the second lens group G2 is moved by the cam mechanism with respectto the imaging sensor 11 from the distance that the third lens group G3is to be moved with respect to the imaging sensor 11. This makes it easyto keep up with fast operation of the zoom ring 84 by the user.

Also, in this embodiment, if a zooming operation is performed from thewide angle end to the telephoto end, with the subject distance atinfinity, the focus lens unit 75 (more precisely, the third lens groupG3, which is a focus lens group) must be moved in the Z axis directionby about 3 mm with respect to the imaging sensor 11. When the focusmotor 64 is driven at 800 pps, the amount of drive of the focus lensunit 75 per rotation of the focus motor 64 is 0.6 mm as mentioned above,so it takes 0.25 second to move the focus lens unit 75 by 3 mm in the Zaxis direction on the basis of the tracking table. Since it is possibleto move the focus lens unit 75 from the wide angle end to the telephotoend in approximately 0.25 second, even if the user should turn the zoomring 84 from the wide angle end to the telephoto end in 0.5 second, thedrive of the focus lens unit 75 can keep up with the change in focallength. Consequently, even if the user should perform a quick zoomingoperation while looking at the subject on the display unit 20 in liveview mode, for example, the subject image that shows on the display unit20 will be unlikely to be blurred, and this makes the camera easier touse.

(3) Focusing Operation

Next, the focusing operation of the digital camera 1 will be described.The digital camera 1 has two focus modes: an auto-focus imaging mode anda manual imaging mode. The user of the digital camera 1 can select thefocus mode with a focus imaging mode setting button (not shown) providedto the camera body 3.

In the auto-focus imaging mode, auto-focus operation is performed bycontrast detection method. When auto-focusing is performed by contrastdetection method, the body microcomputer 10 asks the lens microcomputer40 for contrast AF data. This contrast AF data is necessary inauto-focusing by contrast detection method, and includes, for example,the focus drive speed, focus shift amount, image magnification ratio,and information about whether contrast AF is possible.

The body microcomputer 10 monitors whether or not the shutter button 30has been pressed half way down. If the shutter button 30 has beenpressed half way down, the body microcomputer 10 issues an auto-focuscommencement command to the lens microcomputer 40. This auto-focuscommencement command is to start the auto-focus operation by contrastdetection method. Upon receiving this command, the lens microcomputer 40drives and controls the focus motor 64, which is a focus actuator. Moreprecisely, the lens microcomputer 40 sends a control signal to the focusdrive controller 41. On the basis of this control signal, the focusdrive controller 41 drives the focus motor 64, and the focus lens unit75 moves minutely.

The body microcomputer 10 calculates an evaluation value for auto-focusoperation (hereinafter referred to as an AF evaluation value) on thebasis of the received image data. More specifically, the bodymicrocomputer 10 sends a command to the digital signal processor 15. Thedigital signal processor 15 sends an image signal to the bodymicrocomputer 10 at a specific timing on the basis of the receivedcommand. The body microcomputer 10 finds a brightness signal from theimage data produced by the imaging sensor 11, and finds the AFevaluation value by integrating the high-frequency component within thescreen of the brightness signal. The AF evaluation value thus calculatedis stored in a DRAM (not shown) in a state of being associated with theexposure synchronization signal. Since the lens position informationacquired by the body microcomputer 10 from the lens microcomputer 40 isalso associated with the exposure synchronization signal, the bodymicrocomputer 10 can store the AF evaluation value with it associatedwith the lens position information.

Next, the body microcomputer 10 extracts as the focal point the positionof the focus lens unit 75 where the AF evaluation value is at itsmaximum, on the basis of the AF evaluation value stored in the DRAM. Themethod for driving the focus lens unit 75 in the extraction of the focalpoint is generally known as a hill climbing method. With a hill climbingmethod, the focus lens unit 75 is moved in the direction of increasingthe AF evaluation value, and the AF evaluation value is found for eachposition of the focus lens unit 75. This operation is continued untilthe maximum value for the AF evaluation value is detected, that is,until the AF evaluation value increases up to its peak and the begins todecrease.

The body microcomputer 10 sends a control signal to the focus drivecontroller 41 via the lens microcomputer 40 so that the focus lens unit75 will be driven to the position corresponding to the extracted focalpoint. The focus drive controller 41 produces a drive pulse for drivingthe focus motor 64 on the basis of a control signal from the bodymicrocomputer 10 (or the lens microcomputer 40), for example. The focusmotor 64 is driven by an amount corresponding to this drive signal, andthe focus lens unit 75 moves in the Z axis direction to the positioncorresponding to the focal point.

Focusing in auto-focus imaging mode is performed in this way with thedigital camera 1. The above operation is executed instantly when theuser presses the shutter button 30 half way down.

Focusing by contrast detection method can also be carried out in monitorimaging mode (known as viewfinder mode), in which real-time image datacan be produced with the imaging sensor 11. The reason for this is thatin viewfinder mode, image data is produced in a steady state by theimaging sensor 11, and auto-focusing by contrast detection method usingthis image data is easy.

In viewfinder mode, since a real-time image of the subject is displayedon the display unit 20, the user can decide on the composition fortaking the still picture or moving picture while looking at the displayunit 20. Also, there is another imaging mode the user can select inaddition to live view mode using the display unit 20, which is a secondlive view mode (viewfinder imaging mode) in which the subject image fromthe interchangeable lens unit 2 is guided to the liquid crystalviewfinder 8 (viewfinder unit 38).

The manual focus imaging mode will now be described.

When the user turns the focus ring 89, the focus ring angle detector 90detects the rotational angle of the focus ring 89 and outputs a signalcorresponding to this rotational angle. The focus drive controller 41 isable to receive signals from the focus ring angle detector 90, and ableto send signals to the focus motor 64. The focus drive controller 41sends the decision result to the lens microcomputer 40. The focus drivecontroller 41 drives the focus motor 64 on the basis of a control signalfrom the lens microcomputer 40. More precisely, the lens microcomputer40 produces a drive signal for driving the focus motor 64 on the basisof a focus ring rotational angle signal. When the lead screw 64 a of thefocus motor 64 rotates according to the drive signal, the focus lensunit 75 moves in the Z axis direction via the rack 66 that meshes withthe lead screw 64 a. In the wide angle end state shown in FIGS. 5 and 6,the subject distance is infinity, but as the subject distance drawscloser, the focus lens unit 75 moves to the Z axis direction positiveside. Similarly, in the telephoto end state shown in FIGS. 7 and 8, thesubject distance is infinity, but as the subject distance becomesshorter, the focus lens unit 75 moves to the Z axis direction positiveside. The amount of movement of the focus lens unit 75 is greater inthis case than in the case of the wide angle end.

In this way, the user can perform focusing by turning the focus ring 89while looking at the subject on the display unit 20. In the manual focusimaging mode, when the user presses the shutter button 30 all the waydown, imaging is performed in this unchanged state.

(4) Still Picture Imaging

When the user presses the shutter button 30 all the way down, a commandis sent from the body microcomputer 10 to the lens microcomputer 40 sothat the aperture value of the optical system L will be set to theaperture value calculated on the basis of the light measurement outputof the imaging sensor 11. The aperture drive controller 42 is controlledby the lens microcomputer 40, and the aperture unit 62 is constricted tothe indicated aperture value. Simultaneously with the indication of theaperture value, a drive command is sent from the imaging sensor drivecontroller 12 to the imaging sensor 11, and a shutter unit 33 drivecommand is sent out. The imaging sensor 11 is exposed by the shutterunit 33 for a length of time corresponding to the shutter speedcalculated on the basis of the light measurement output of the imagingsensor 11.

The body microcomputer 10 executes imaging processing and, when theimaging is completed, sends a command signal to the image recordingcontroller 19. The image recorder 18 records an image signal to aninternal memory and/or removable memory on the basis of the command ofthe image recording controller 19. The image recorder 18 records imagingmode information (whether auto-focus imaging mode or manual focusimaging mode) along with the image signal to the internal memory and/orremovable memory on the basis of the command of the image recordingcontroller 19.

Upon completion of the exposure, the imaging sensor drive controller 12reads image data from the imaging sensor 11, and after specific imageprocessing, image data is outputted via the body microcomputer 10 to theimage display controller 21. Consequently, the captured image isdisplayed on the display unit 20.

Also, upon completion of the exposure, the shutter unit 33 is reset toits initial position by the body microcomputer 10. The bodymicrocomputer 10 issues a command to the lens microcomputer 40 for theaperture drive controller 42 to reset the aperture unit 62 to its openposition, and a reset command is sent from the lens microcomputer 40 tothe various units. Upon completion of this resetting, the lensmicrocomputer 40 tells the body microcomputer 10 that resetting iscomplete. After the resetting completion information has been receivedfrom the lens microcomputer 40, and after a series of post-exposureprocessing has been completed, the body microcomputer 10 confirms thatthe shutter button 30 is not being pressed, and the imaging sequence isconcluded.

(5) Moving Picture Capture

The digital camera 1 also has the function of capturing moving pictures.In moving picture imaging mode, image data is produced by the imagingsensor 11 at a specific period, and the image data thus produced isutilized to continuously carry out auto-focusing by contrast detectionmethod. In moving picture imaging mode, if the shutter button 30 ispressed, or if the moving picture capture operation button 24 ispressed, a moving picture is recorded to the image recorder 18, and whenthe shutter button 30 or the moving picture capture operation button 24is pressed again, recording of the moving picture by the image recorder18 is stopped.

Features of Digital Camera

The features of the digital camera 1 described above are as follows.

(1) With this digital camera 1, the photosensor 67 can detect whether ornot the focus lens unit 75 is disposed at the starting point position Dwith respect to the second lens group unit 77. Furthermore, the startingpoint position D is disposed within the total movement range E. As aresult of this constitution, the drive time it takes to move the focuslens unit 75 from the starting point position D to a specific positionwithin the total movement range E can be shorter. Consequently, thestart-up time can be reduced with this digital camera 1.

(2) With this digital camera 1, three tracking tables 100 are used astracking information, the starting point position D is disposed withinthe movement range G of the focus lens unit 75 based on the trackingtables 100 with a subject distance of infinity and 1 m, and the startingpoint position D is not disposed in the movement range of the trackingtable 100 with a subject distance of 0.3 m. When there is thus a highprobability of use of one of the tracking tables 100, the drive time formoving the focus lens unit 75 from the starting point position D to aspecific position can be made shorter by disposing the starting pointposition D within the movement range of the focus lens unit 75 based onone of the tracking tables 100.

For example, with this digital camera 1, the starting point position Dis disposed in the movement range G of the focus lens unit 75 based onthe infinity tracking table 100. In general, the user is most likely tocapture an image of a subject at the infinity position when turning onthe power to the digital camera 1 and capturing an image of the subject,so the start-up time can be shortened by disposing the starting pointposition D within the movement range G.

(3) With this digital camera 1, since the starting point position D isdisposed in the middle of the total movement range E, the drive time canbe shortened when moving the focus lens unit 75 to any position withinthe total movement range E.

(4) With this digital camera 1, the movement range H of the focus lensunit 75 based on the infinity tracking table 100 includes the movementrange H from the position H2 corresponding to the wide angle end to theposition H1 at which the focus lens unit 75 is farthest away from theimaging sensor 11. The starting point position D is disposed in themiddle of this movement range H. In general, the optical system L ismost likely to be at the wide angle end when the user turns on the powerto the digital camera 1 and captures an image of the subject, so thestart-up time can be shortened by disposing the starting point positionD in the middle of the movement range H.

Other Embodiments

Embodiments are not limited to those discussed above, and variouschanges and modifications are possible without departing from the gistof the present invention. Also, the above embodiment are basically justfavorable examples, and are not intended to limit the present invention,its applications, or the scope of these applications.

(1) In the above embodiment, the digital camera 1 was capable ofcapturing both moving and still pictures, but may instead be capable ofcapturing just still pictures, or just moving pictures.

(2) In the above embodiment, the digital camera 1 may be, for example, adigital still camera, a digital video camera, a mobile telephoneequipped with a camera, or a PDA equipped with a camera.

(3) Although the above-mentioned digital camera 1 was not described asincluding a quick return mirror, it may have a quick return mirrorsimilar to conventional single reflex lens cameras.

(4) The configuration of the optical system L is not limited to that inthe above embodiment. For example, the third lens group G3 may be madeup of a plurality of lenses, and the second lens group G2 may be made upof just a single lens. Also, the layout of the optical system L is notlimited to that shown in FIGS. 12A-12B.

(5) In the above embodiment, the exposure time to the imaging sensor 11was controlled by operating the shutter unit 33, but the exposure timeof the imaging sensor 11 may instead be controlled by an electronicshutter.

(6) In the above embodiment, electronic tracking was performed by thelens microcomputer 40, but a command may be sent from the bodymicrocomputer 10 to the lens microcomputer 40, and the control of theelectronic tracking performed on the basis of this command.

(7) In the above embodiment, the starting point position D was disposedin the middle of the movement range H, but as shown in FIG. 15, thestarting point position D may be disposed in the middle of the movementrange G. Here again, the start-up time can be shortened because thestarting point position D is determined using as a reference thetracking table 100 in which the subject distance is infinity.

(8) In the above embodiment, the starting point position D wasdetermined using as a reference the tracking table 100 in which thesubject distance was infinity, but another tracking table 100 may beused instead. For example, as shown in FIG. 16, the starting pointposition D may be determined using as a reference the tracking table 100in which the subject distance is 0.3 m.

More specifically, as shown in FIG. 16, the starting point position D isdisposed within a movement range J (between a position JT and a positionJ2; an example of the first tracking range) of the focus lens unit 75based on the tracking table 100 in which the subject distance is 0.3 m.More precisely, the starting point position D is disposed in the middleof the movement range J. The position J2 is the position of the focuslens unit 75 corresponding to the wide angle end. The position JT is theposition where the focus lens unit 75 is farthest away from the imagingsensor 11.

For example, if the optical system L is an optical system used for macroimaging, it is most likely that the imaging will take place at theshortest subject distance of 0.3 m, so the start-up time can beshortened by disposing the starting point position D in the middle ofthe movement range J.

(9) In the above embodiment, the starting point position D was disposedin the middle of the total movement range E, but the starting pointposition D may be shifted from the middle of the total movement range Eto the extent that the start-up time can still be shortened. That is,the starting point position D may be disposed substantially in themiddle of the total movement range E.

Also, the starting point position was disposed in the middle of themovement range H, but the starting point position D may be shifted fromthe middle of the movement range H to the extent that the start-up timecan still be shortened. That is, the starting point position D may bedisposed substantially in the middle of the movement range H.

Furthermore, the starting point position D may be shifted from themiddle of the movement range J to the extent that the start-up time canstill be shortened. That is, the starting point position D may bedisposed substantially in the middle of the movement range J.

(10) The tracking tables 100 shown in FIGS. 14 to 16 are examples, andthe tracking tables are not limited to the tracking tables 100 discussedabove. In the above embodiment, although the tracking table in which thesubject distance was infinity (∞) is arranged at a closest position tothe imaging element in FIGS. 14 to 16 (that is, at a lowest position inFIGS. 14 to 16), the tracking table in which the subject distance isshort, such as 0.3 m, may be arranged at a closest position to theimaging element in FIGS. 14 to 16. With such optical system, the effectwill be the same as that in the embodiments given above.

While only selected embodiments have been chosen to illustrate thepresent invention, it will be apparent to those skilled in the art fromthis disclosure that various changes and modifications can be madeherein without departing from the scope of the invention as defined inthe appended claims. Furthermore, the foregoing descriptions of theembodiments according to the present invention are provided forillustration only, and not for the purpose of limiting the invention asdefined by the appended claims and their equivalents. Thus, the scope ofthe invention is not limited to the disclosed embodiments.

1. A lens barrel for forming an optical image of a subject on an imagingelement, comprising: a first lens unit having a first lens element and afirst lens support frame supporting the first lens element; a secondlens unit having a second lens element arranged to vary the focal lengthby moving relative to the first lens element in the optical axisdirection, and a second lens support frame supporting the second lenselement; a focus lens unit having a focus lens arranged to vary thefocal state of the optical image by moving relative to the first lenselement or the second lens element in the optical axis direction, and afocus lens support frame supporting the focus lens; a zoom mechanismarranged to relatively move the first lens unit and the second lens unitin the optical axis direction, having a zoom operating unit arranged tobe operated by the user, with which the operating force inputted to thezoom operating unit is mechanically transmitted to at least one of thefirst lens unit and the second lens unit; a focus actuator supported bythe zoom mechanism to move integrally with the first lens unit, andconfigured to utilize electric power to drive the focus lens unit in theoptical axis direction with respect to the first lens unit; a startingpoint detector configured to detect whether or not the focus lens unitis disposed at a starting point position with respect to the first lensunit; and a drive controller configured to control the focus actuator sothat the focus lens unit moves within a tracking range including thestarting point position.
 2. The lens barrel according to claim 1,wherein the drive controller is configured to control the focus actuatoron the basis of preset tracking information, the tracking informationcomprises a first tracking table with which the focus actuator can becontrolled so that the in-focus object distance is kept substantially ata first subject distance even if the focal length changes, and a secondtracking table with which the focus actuator can be controlled so thatthe in-focus object distance is kept substantially at a second subjectdistance even if the focal length changes, when the focus actuator iscontrolled by the drive controller on the basis of the first trackingtable, the focus lens unit is arranged to move in the optical axisdirection within a first tracking range, and the starting point positionis disposed within the first tracking range, which is at least part ofthe tracking range.
 3. The lens barrel according to claim 1, wherein thestarting point position is disposed substantially in the middle of thetracking range in the optical axis direction.
 4. The lens barrelaccording to claim 2, wherein the starting point position is disposedsubstantially in the middle of the first tracking range in the opticalaxis direction.
 5. The lens barrel according to claim 2, wherein thefirst subject distance of the first tracking table is infinity.
 6. Thelens barrel according to claim 5, wherein the first tracking range is arange from a first position, at which the focal point can be infinity ina state in which the focal length is the wide angle end, to a secondposition, at which the focus lens unit is farthest away from the imagingelement when the focus lens unit is driven on the basis of the firsttracking table.
 7. The lens barrel according to claim 2, wherein thefirst subject distance of the first tracking table is shorter than thesecond subject distance.
 8. The lens barrel according to claim 2,wherein the first subject distance of the first tracking table is theshortest of all the subject distances in the tracking tables included inthe tracking information.
 9. An imaging device, comprising: the lensbarrel according to claim 1; and a camera body having the imagingelement.
 10. The lens barrel according to claim 2, wherein the startingpoint position is disposed substantially in the middle of the trackingrange in the optical axis direction.
 11. A lens barrel for forming anoptical image of a subject on an imaging element, comprising: a linearposition sensor detecting a rotational position of a zoom ring whichmoves one of a first lens unit and a second lens unit in an optical axisdirection to vary a focal length; a focus lens unit position sensordetecting a position of a focus lens unit, the focus lens unit having afocus lens arranged to vary the focal state of the optical image bymoving relative to a first lens element of the first lens unit or asecond lens element of the second lens unit in the optical axisdirection; a focus actuator configured to utilize electric power todrive the focus lens unit in the optical axis direction with respect tothe first lens unit; a controller coupled to the focus actuator, thelinear position sensor, and the focus lens unit position sensor; a firstmemory portion including a tracking table defining a relationshipbetween a position of the focus lens and the rotational position of thezoom ring; and a second memory portion coupled to the controller, thesecond memory portion including instructions for configuring thecontroller to control the focus actuator so that the position of thefocus lens unit conforms to changes in the focal length in accordancewith the tracking table.
 12. The lens barrel according to claim 11,wherein the tracking table contains information indicating the positionsof the focus lens unit at which a focused subject distance remainssubstantially constant when the focal length changes.
 13. The lensbarrel according to claim 11, wherein the tracking table containsinformation indicating the positions of the focus lens unit at which thefocused subject distance remains substantially constant when the focallength changes for specific subject distance categories.
 14. The lensbarrel according to claim 11, wherein the controller is configured tocontrol the focus actuator so that a starting position of the focus lensunit is substantially in a midpoint of a range of positions of the focuslens unit in the tracking table.